Retort and method for the extraction of zinc



July 26, 1966 F WTHTIHIIIIIIHIHII v. E. CLIFTON 3,262,774

REIORT AND METHOD FOR THE EXTRACTION OF ZINC Filed July 5. 1963 lllllllllllll lllllllllLlll II lllllll llllllll L F ll llllllllllllllllllllllllI United States Patent 3,262,774 RETORT AND METHOD FOR THE EXTRACTION OF ZINC Victor Ernest Clifton, Avonniouth, England, assignor to The National smelting Company Limited, London, England Filed July 5, 1963, Ser. No. 292,970 Claims priority, application Great Britain, July 30, 1962, 29,239/62 6 Claims. (Cl. 75-86) This invention relates to an improvement in a vertical retort installation, e.g. such as is used for the extraction of zinc from its ores.

In the vertical retort process for extraction of zinc, briquettes consisting mainly of compressed zinc oxide together with a pulverised carbonaceous reducing agent pass down a vertical retort which is externally heated by gas firing. The briquettes are charged at the top of the retort, reduction takes place within the retort and the zinc metal formed is volatilised off.

The retorts are usually constructed of refractory brickwork and are rectangular in horizontal cross-section. The residues are continuously removed from the bottom of each retort by means of an extractor roll or spider, which has the form of a cylinder with pockets or hollows cut out of the curved surface and can be made as a number of sections mounted on a horizontal shaft. The rate at which the residues are removed depends upon the rate at which this roll revolves, the size of the pockets and the clearance between the circumferential surface of the roll and the bottom edge of a steel plate known as the extractor plate. It is known to arrange this clearance to be constant along the whole width of the retort.

By means of a freezing test, in which a retort was cooled down whilst full of charge and zinc analyses made at a number of levels and at various points within rectangular horizontal sections, it has been found that the zinc content is much higher in the centre of each rectangular section, at whatever level is tested, than it is at the ends or sides of such a section.

Model work has shown that the rate of descent of charge in a retort is more rapid in the centre than at the ends and the above distribution is presumably a consequence of this. It should be noted that the low zinc contents at the ends and sides do not compensate for the high values near the centre since the charge in the ends and sides of the retort is already completely reduced at a considerable distance above the base (e.g. some seven feet in a conventional installation) and no more work can be done on it below this level. It is therefore to be expected that, if the flow pattern in the retort could be altered so as to produce a more even zinc distribution over the rectangular section at the bottom, the retort could be run at a higher charge rate without increasing the overall zinc in residue, this normally being run at a predetermined value.

It has now been discovered that the flow pattern of the charge in the retort can be altered so as to improve the uniformity of the zinc distribution by altering the cross-sectional shape of the retort, and that the improvement gained is not confined to the lower regions of the retort.

The invention consists in a continuously operable vertical retort installation, in which the retort has an internal horizontal cross-section having two opposing long edges which are inwardly curved.

Preferably the retort has an internal horizontal crosssection in the shape of a rectangle with inwardly curved long edges.

If required, the special cross-section may only extend Ice over a central portion of the retort, as described more fully below.

The invention still further consists in a method of extraction of zinc in which zinc is distilled from such a retort installation.

Although reduction of retort width (i.e. the smaller dimension of the rectangular or near-rectangular section mentioned above) is known to improve the penetration of heat to the briquettes at the centre of the retort, such a reduction of width would in itself make a flow pattern of a strictly rectangular retort worse. Inward bowing according to the invention enables an improved flow pattern and a smaller average width to be achieved.

The invention will be further described with reference to the accompanying drawing, in which:

FIGURE 1 is a vertical section through a vertical retort according to the invention.

FIGURE 2a is a horizontal section at AA of FIG- URE 1.

FIGURE 2b is a horizontal section at BB of FIG- URE l, and at DD of FIGURE 1, the two sections being the same in reverse order, and

FIGURE 2c is a horizontal section at C-C of FIG- URE 1.

In this embodiment, the horizontal cross-section at the top region 1 of the-retort R is rectangular, as shown in FIGURE 2a. This rectangular cross-section gradually changes, over region 2, by the side walls coming close together at the centre (FIGURE 2b) until at region 3 (FIGURE 2c) the side walls are appreciably curved. The cross-section gradually reverts over region 4 to a rectangular section again at the bottom of the retort 5.

By way of example, the rectangular inner area at regions 1 and 5 may be about eight feet by twelve inches, while in region 3 the side walls may approach to within ten inches of one another at the centre although still being twelve inches apart at the ends. The overall height of a retort is usually 25 to 30 feet.

Inwardly bowed walls according to the invention have various advantages over parallel walls.

(1) The main advantage is that the briquette flow pat tern may be controlled, i.e. the briquettes at the retort middle may be prevented from travelling too fast relative to those at the ends. This leads tomore even reduction of the briquettes and consequently to a smaller loss of zinc in residues (or alternatively to a greater output for a given residue zinc target).

(2) Heat transfer to the centre of the retort is improved and the briquettes are reduced more efiiciently by using a retort which is, on the average, of smaller area of cross-section.

(3) In relation to the mechanical pressure exerted by the briquettes upon the inner surfaces of the walls, inwardly bowed walls are inherently stronger. They are therefore less likely to bow outwards during use and therefore to lose efliciency or to crack.

Various modifications may be made within the scope of the invention as defined in the appended claims.

I claim:

1. In an externally heated retort for the pyrometallurgical reduction of zinciferous material having vertical end and side walls of a refractory material, the interior of said retort being generally rectangular in cross-sectional configuration, the improvement, in combination therewith, comprising an intermediate section of said retort having at least one side wall arched inwardly to form a constricted interior cross-sectional portion of the retort.

2. An externally heated retort according to claim 1, in which both opposite side walls of the intermediate sectitLn of the retort are arched inwardly towards each ot er.

3. An externally heated retort according to claim 1,

section having substantially parallel opposed side walls positioned on each side of said intermediate section.

4. An externally heated vertical retort for the pyrometallurgical reduction of zinciferous material having at least four superposed regions of successively different internal cross-sectional areas, running from the top to the bottom of the retort:

(a) region 1 is generally rectangular in interior crosssection, with its end and side walls vertically disposed, the end walls being parallel to each other;

(b) region 2 has its side walls gradually arch-ed inwardly towards each other from the top to the bottom of this region, so that the cross-sectional area of the interior portion of the retort is gradually and correspondingly narrowed;

(0) region 3 has its side walls arched inwardly towards each other so that the cross-sectional area of the interior portion of the retort is narrowed substantially the same amount throughout the entire height of this region; and

((1) region 4 has its side walls arched inwardly at its upper portion, but the amount of arch is gradually reduced until the side walls revert to a generally rectangular cross-section at the bottom of the retort proper.

5. In the method of subjecting an elongated column of compressed briquettes formed of a mixture of oxidic zinciferous material and pulverized carbonaceous reducing agent to pyrornetallurgical reduction as the column moves by gravity downward through an elongated externally heated retort having an elongated vertical reduction zone of generally rectangular cross-sectional interior configuration, volatilizing the resulting zinc, and removing the zinc vapors from the retort and the reduction zone, the improvement in combination therewith which comprises: the pattern of flow of the briquettes through the retort is changed by causing them to advance through at least one constricted portion in an intermediate section of the elongated vertical reduction Zone.

6. In the method of externally heating a continuous column of compressed briquettes formed of mixed oxidic zinciferous material and pulverized carbonaceous reducing agent in a vertical generally rectangular reduction zone of an externally heated retort as the column of briquettes moves downwardly by gravity through the retort, the improvement in combination therewith which comprises: advancing the upper section of the column of briquettes through the upper section of the reduction zone, the upper section or" said zone having a substantially uniform cross-sectional area; advancing an intermediate section of a column of briquettes through an elongated intermediate section of the reduction zone, said intermediate zone having a constricted smaller cross-sectional area than that of the upper section; and advancing a lower section of the column of briquettes through a lower section of the reduction zone, the lower section of the reduction zone having a cross-sectional area substantially the same as that of the upper section.

References Cited by the Examiner UNITED STATES PATENTS 1,887,453 11/1932 Emmel 266 25 2,013,980 9/1935 Bunce 75-86 2,132,858 10/1938 Matthies 75-86 2,338,781 1/1944 Porter 22-572 2,676,095 4/ 1954 Be Vaney 266-25 2,718,096 9/ 1955 Henry 266-25 OTHER REFERENCES Henderson, Metallurgical Dictionary, Reinhold Publishing Co., 1953.

DAVID L. RECK, Primary Examiner.

H. \V. CUMMINGS, H. TARRING, Assistant Examiners. 

1. IN AN EXTERNALLY HEATED RETORT FOR THE PYROMETALLURGICAL REDUCTION OF ZINCIFEROUS MATERIAL HAVING VERTICAL END AND SIDE WALLS OF A REFRACTORY MATERIAL, THE INTERIOR OF SAID RETORT BEING GENERALLY RECTANGULAR IN CROSS-SECTIONAL CONFIGUATION, THE IMPROVEMENT, IN COMBINATION THEREWITH, COMPRISING AN INTERMEDIATE SECTION OF SAID RETORT HAVING AT LEAST ONE SIDE WALL ARCHED INWARDLY TO FORM A CONSTRICTED INTERIOR CROSS-SECTION PORTION OF THE RETORT. 